Automatic decompression system

ABSTRACT

An automatic decompression system for an internal combustion engine, especially a one-cylinder diesel engine, with at least one outlet and one inlet valve, which are activated by a camshaft ( 20 ) with at least one cam ( 1 ), wherein the outlet valve is lifted during starting to reduce the cranking resistance, wherein there is provided for lifting the outlet valve at speeds below a switching speed for changeover from decompression to compression a fully automatic lifting device, which engages in the cam ( 1 ) of the outlet valve and effects lifting of the outlet valve from the valve seat, wherein the lifting device is equipped with a bow-shaped member ( 22 ), pivoted in articulated relationship, disposed between cam ( 1 ) and a cam disk ( 2 ), which bow-shaped member has two articulated arms ( 11 ) and a crosspiece ( 14 ) joining them, and which at speeds below the switching speed occupies in the cam plane an engaged decompression position, in which it projects beyond the cam base circle, and which can be disengaged into a neutral position in the cam-disk plane when the switching speed is reached, is provided for the purpose of speed-dependent control of the engagement and disengagement process with at least one flyweight ( 3 ), which is subjected by a spring ( 5 ) to radially inward pressure and which is coupled flexibly with the bow-shaped member.

The subject matter of the present invention is an automaticdecompression system for an internal combustion engine, especially aone-cylinder diesel engine, with at least one outlet and one inletvalve, which are activated by a camshaft with at least one cam, whereinthe outlet valve is lifted during starting to reduce the crankingresistance and with further features according to the preamble of claim1.

From the prior art there are known devices which reduce the crankingresistance during starting of internal combustion engines. Most aresemi-automatic devices which lift the outlet valve by a few tenths ofone millimeter by a manually operated lever and, after one working cycleduring reversing start or after several working cycles duringhand-cranked start, switch from decompression to compression by means ofa restoring or latching mechanism. Also known from the prior art aredecompression devices which, under centrifugal control, lift only one ofthe valves (inlet or outlet valve) by a few tenths of one millimeter fora specified, short angular range around ignition TDC and, when aspecified crankshaft speed is reached, switch again from decompressed tocompressed condition. Yet another starting aid operating undercentrifugal control is known from European Patent EP 0515183 A1. Becauseof the rigid connection between flyweight and bow-shaped member, arelatively large installation space is needed this device. The object ofthe present invention is therefore to provide an easy-to-make, low-costautomatic decompression system which operates completely automaticallyby purely mechanical regulation and needs only a small installationspace. This object is achieved by the automatic decompression system ofthe present invention. Therein there is provided for lifting the outletvalve at speeds below a switching speed for changeover fromdecompression to compression a fully automatic lifting device, whicheffects lifting of the outlet valve from the valve seat. In this way thelifting device effects lifting of the valve as long as the camshaft isrotating more slowly than a specified switching speed. This leadsadvantageously to reduction of the cranking resistance during starting,whereby the internal combustion engine is started either manually byreversing cable or by crank or electrically by means of a small startermotor. Above the switching speed the lifting device is inactive, and sothe valve is not lifted and thus full compression takes place.Furthermore, the invention provides that the lifting device is equippedwith a bow-shaped member, pivoted in articulated relationship, disposedbetween the cam and a cam disk, which bow-shaped member has twoarticulated arms and a crosspiece joining them, and which at speedsbelow the switching speed occupies in the cam plane an engageddecompression position, in which it projects beyond the cam base circle,and which can be disengaged into a neutral position in the cam-diskplane when the switching speed is reached. This bow-shaped member isdesigned such that it can swivel around a rotary pivot disposed in aplane parallel to the cam plane and, in fact, in such a way that thebow-shaped member is engaged in the cam plane with the crosspiecedisposed transverse to the articulated arms and projects beyond the cambase circle when the camshaft is turning slowly or is stopped. By thisspace-saving arrangement, the valve is slightly lifted from its closedposition, or in other words raised from the valve seat, as long as it iscontrolled by the cam in the region of the crosspiece. After thespecified switching speed has been reached, a restoring force is exertedon the articulated arms, causing swiveling movement of the bow-shapedmember, whereby the crosspiece is disengaged into the cam-disk plane.Hereby there is created in simple manner with purely mechanical means acompletely automatic decompression system, which has only a small spacerequirement in the assembly chamber. Furthermore, the invention providesthat, for speed-dependent control of the engagement and disengagementprocess of the bow-shaped member for decompression or compressionrespectively, there is provided at least one flyweight held in aspecified rest position by a pretensioning spring and subjected inradial direction to inward pressure. The mass of this flyweight isdimensioned such that it occupies its outermost radial position againstthe pressure of the spring at the defined switching speed, or in otherwords such that it bears against a stop in this position. In addition,the pretensioning spring ensures that the flyweight when in restposition is held in a specified position regardless of gravitationalforces. In dimensioning the mass of the flyweight as a function ofswitching speed, the pretensioning force of the spring must be takeninto consideration. By the coupling of the flyweight mechanism with thebow-shaped member pivoted in articulated relationship, engagement anddisengagement of the bow-shaped member as a function of switching speedis achieved in simple manner.

In this connection an advantageous embodiment of the invention providesthat the inside radius of one of the flyweights is shaped as a ramp toengage the bow-shaped member against the resistance of a disengagingspring. In this structural embodiment, the turning knuckle of thebow-shaped member is disposed approximately at the height of thelongitudinal axis of the camshaft parallel to the cam plane. For thispurpose the articulated arms are provided with a lever arm extending tothe crosspiece and a lever arm extending from the joint in the directionopposite the crosspiece. The lever arm is loaded by the disengagingspring, whereby the bow-shaped member is held in its disengaged positionas long as the flyweight occupies its outermost radial position atspeeds above the switching speed. At speeds of rotation below theswitching speed, the ramp-like face of the inside radius of theflyweight bears against the crosspiece, causing the bow-shaped member tobe held in its engaged position against the pretension exerted by thedisengaging spring.

A further advantageous embodiment of the present invention provides thatthe flyweight is coupled with the bow-shaped member via a driverdisposed on the articulated arm. In this embodiment, the driver,designed as a lever, is coupled directly with a driving arm of theflyweight. When the switching speed is reached, the flyweight drives thedriver to the extent that the bow-shaped member tilts outward to itsdisengaged position and becomes positioned in the cam-disk plane. Belowthe switching speed, the driving arm holds the bow-shaped member in itsengaged position, in which the crosspiece is disposed in the cam plane.

Finally, it is advantageous for two bow-shaped flyweights to beprovided, which are coupled with each other by a joint. Hereby theinfluence of gravitational forces is advantageously eliminated by therestraining effect of two opposite flyweights. Thereby it is possible toachieve very low switching speeds, which is advantageous in particularfor reversing starts.

Another advantageous embodiment of the invention provides that liftingin decompression position takes place in a specified crank-angle rangeof approximately 90° by appropriate arc length of the bow-shaped member.This is the range available after closing of the inlet valve and beforeattainment of ignition TDC or after ignition TDC and before opening ofthe outlet valve. For reasons of valve-play adjustment capability, arange without valve lift must be provided at ignition TDC.

Furthermore, it is advantageous for the switching speed to be between300 and 600 rpm, preferably 400 rpm. By selecting such a switchingspeed, manual starting is still possible even at extremely lowtemperatures, or the engine can be turned with a low-power starter.

Finally, an advantageous embodiment provides that the control cam isprovided with a slot to accommodate the bow-shaped member in engagedposition. Hereby the bow-shaped member retains its specified positionand is protected from deformation.

Yet another advantageous further embodiment of the present inventionprovides that the inlet valve can be actuated via the same cam as theoutlet valve and, in the direction of rotation of the camshaft after theoutlet valve, is lifted in addition thereto during the decompressionphase. Therein lies the advantage that, in combination with reversing orkick-start devices, the cranking resistance is reduced by the proportionof charge-changing work to be expended for the suction stroke. Therebyit is also ensured that no unfiltered intake can take place from theexhaust line.

Finally, it is advantageous for the closing of the outlet valve to takeplace 40° before ignition TDC and the opening of the inlet valve 40°after ignition TDC. Thereby both valves are reliably closed at ignitionTDC.

Finally, a further embodiment of the present invention provides that avalve-dragging lever is provided between cam and valve. This canactivate the valve directly or via a tappet rod.

Finally, it is advantageous for the valve-dragging lever to be liftableby 0.2 mm to 0.6 mm, preferably 0.4 mm, by the lifting device. Dependingon movement ratio, this causes lifting of the valves by between 0.3 and0.8 mm.

Advantageous embodiments of the present invention will be explained inmore detail hereinafter with reference to the attached figures, wherein:

FIG. 1 shows a front view of a first embodiment of the automaticdecompression system according to the invention;

FIG. 2 shows a cutaway side view of the automatic decompression systemaccording to FIG. 1;

FIG. 3 shows a front view of the automatic decompression systemaccording to FIG. 1, wherein the inlet valve is lifted;

FIG. 4 shows an automatic decompression system according to FIG. 1 afterthe switching speed has been reached;

FIG. 5 shows a cutaway side view of the automatic decompression systemaccording to FIG. 1 after the switching speed has been reached;

FIGS. 6a-6 c show different embodiments of a bow-shaped member accordingto the invention;

FIG. 7 shows a further embodiment of the automatic decompression systemaccording to the invention in cutaway side view;

FIG. 8 shows a valve-control characteristic diagram with decompression.

FIG. 1 shows a front view of a first embodiment of the automaticdecompression system according to the invention with cam 1 disposed oncamshaft 20 and a cam disk 2. In the cam-disk plane there are pivoted afirst flyweight 3, which is pivoted at a point 4 and is pressed radiallyinward by a spring 5, a second flyweight 6 with a further bearing point7 and the common joint 8 as well as driving arm 9 and bow-shaped member22. Driver 10, articulated arm 11 joined thereto, second articulated arm13 and crosspiece 14 form bow-shaped member 22. Toothing 15 of cam disk2 as well as cam base circle are indicated by a dot-dash line. Alsorepresented by dot-dash lines are dragging lever 16 for the outlet valveand dragging lever 17 for the inlet valve. Also illustrated are nose 18of first flyweight 3 as well as nose 19 of second flyweight 6, each ofwhich is disposed at the ends of the bow-shaped flyweights oppositebearing points 4 and 7.

Hereinafter like parts will be denoted by like reference symbols.

FIG. 2 shows a cutaway side view of the automatic decompression systemaccording to FIG. 1. Therein only dragging lever 16 of the outlet valveis illustrated. This is provided with a sliding face 21, which bears oncam 1 and, depending on the lifting movement thereof, opens or closesthe outlet valve. On both articulated arms, bow-shaped member 22 withcrosspiece 14 and articulated arm 11 as well as driver 10 is pivoted inswiveling relationship on a bearing 23 in cam disk 2. Also illustratedare camshaft 20, first flyweight 3 and second flyweight 6 as well astoothing 15 of cam disk 2.

FIGS. 1 and 2 describe a condition of the automatic decompression systemwhen it is stopped or rotating at speeds below the switching speed. Inthis condition, first flyweight 3 is pressed radially inward by spring 5and second flyweight 6 is also held in radially inward direction viaarticulated joint 8. Hereby driving arm 9 holds driver 11 in a positiondistant from camshaft axis 24, whereby crosspiece 14 of bow-shapedmember 22 is disposed in engaged position in the camshaft plane. When aswitching speed is reached, the centrifugal force of the two flyweights3 and 6 is greater than the radially inward force of spring 5, wherebythe flyweights are forced radially outward until noses 18 and 19 arestopped against slot bottom 25 of the cam disk. In this condition,driver 10 is moved into a position close to axis 24 of the camshaft,whereby bow-shaped member 22 is disengaged into a neutral position inthe cam-disk plane. This condition is illustrated in FIGS. 4 and 5.

In the engaged condition, crosspiece 14 engages in a slot 26 of cam 1,whereby crosspiece 14 of bow-shaped member 22 projects by a few tenthsof one millimeter beyond cam base circle N. If the cam disk from FIG. 1now turns further clockwise, the engaged bow-shaped member first liftsdragging lever 17 of the inlet valve by a few tenths of one millimeter,the effective crank-angle range being determined by the arc length ofbow-shaped member 22, or in other words by the length of crosspiece 14.This condition is illustrated in FIG. 3. When further turned, cam 1first opens the outlet valve and then the inlet valve and, after theoutlet valve has closed, lifts it slightly again by the engagedbow-shaped member. This engagement and disengagement of the bow-shapedmember takes place, as already described, under centrifugal control,wherein engagement during reengagement can take place only if thebow-shaped member is not disposed exactly at the height of a dragginglever.

FIGS. 6a to 6 c show side views of various embodiments of a bow-shapedmember according to the invention. Therein not only articulated arm 11and crosspiece 14 but also driver 10 and a knife edge 23 functioning asa joint are illustrated. FIG. 6b shows a bow-shaped member in which thebearing is formed by a ball 60. FIG. 6c finally shows the side view ofan embodiment of a bow-shaped member according to the invention, whereinthe bearing is formed by a pivot 61.

FIG. 7 shows a further embodiment of an automatic decompression systemaccording to the invention. This is distinguished from the embodimentdescribed hereinabove on the one hand by the fact that first flyweight70 is provided with an inside radius designed as a ramp 71, and on theother hand by the fact that bow-shaped member 72 can be swiveled arounda pivot 73 passing through the centerline of the camshaft. Bow-shapedmember 72 is provided not only with articulated arm 74 and crosspiece 75but also lever arm 76, which is loaded by a spring 77. Hereby, at speedshigher than the switching speed, the bow-shaped member is disengaged andheld in this position. Below the switching speed, the bow-shaped memberis pushed by ramp 71 against the spring force of spring 77 into itsengaged position in the cam plane and held in this position until theflyweight drifts outward once again.

FIG. 8 shows a valve-control characteristic diagram of decompression, inwhich 100 denotes the valve-height curve of the outlet valve, 102 thevalve-height curve of the inlet valve, 103 the valve height due to theautomatic decompression system at the inlet valve, and 104 the valveheight due to the automatic decompression system at the outlet valve.Ignition TDC is denoted by 105 and the overlap TDC by 106. It is clearlyevident from this characteristic diagram that no lifting of the valvetakes place approximately 40° before ignition TDC and 40° after ignitionTDC.

What is claimed is:
 1. An automatic decompression system for an internalcombustion engine with at least one outlet valve and one inlet valvewhich are activated by a camshaft having at least one cam, and whereinsaid at least one outlet valve is lifted from its valve seat duringstarting to reduce cranking resistance, said system comprising: a fullyautomatic lifting device for lifting the at least one outlet valve atspeeds below a switching speed for change over from compression todecompression, which fully automatic lifting device engages in the camof the at least one outlet valve and effects lifting of the at least oneoutlet valve from its valve seat, wherein the fully automatic liftingdevice is equipped with a bow-shaped member pivoted in articulatedrelationship and disposed between the at least one cam and a cam disk,which bow-shaped member has two articulated arms pivoted at points in aradial plane of the cam disk and connected by a crosspiece, and whereinat engine speeds below the switching speed said bow-shaped memberoccupies in the cam plane an engaged decompression position, in whichsaid bow-shaped member projects beyond the cam base circle, and when theswitching speed is reached said bow-shaped member can be disengaged intoa neutral position in the cam-disk, and wherein at least one flyweightis coupled to the bow-shaped member and biased by a spring in a radialdirection to control the engagement and disengagement of the bow-shapedmember depending on the engine speed.
 2. An automatic decompressionsystem according to claim 1, wherein an internal radius of the flyweightis designed as a ramp for engaging the bow-shaped member against theresistance of a disengaging spring thereby coupling the flyweight to thebow-shaped member.
 3. An automatic decompression system according toclaim 1, wherein the flyweight is coupled with the bow-shaped member viaa driver disposed on an articulated arm.
 4. An automatic decompressionsystem according to claim 1, wherein two bow-shaped flyweights areprovided, which are connected to each other by a joint.
 5. An automaticdecompression system according to claim 1, wherein lifting indecompression position takes place in a specified crank-angle range ofapproximately 90° by appropriate arc length of the bow-shaped member. 6.An automatic decompression system according to claim 1, wherein theswitching speed is between 300 and 600 rpm.
 7. An automaticdecompression system according to claim 1, wherein the control cam isprovided with a slot to accommodate the bow-shaped member in engagedposition.
 8. An automatic decompression system according to claim 1,wherein the inlet valve can be actuated via the same cam as the outletvalve and, in the direction of rotation of the camshaft after the outletvalve, is lifted in addition thereto during the decompression phase. 9.An automatic decompression system according to claim 1, wherein theoutlet valve is closed 40° before ignition TDC and the inlet valve isopened 40° past ignition TDC.
 10. An automatic decompression systemaccording to claim 1, wherein a valve-dragging lever is provided betweensaid at least one cam and valve.
 11. An automatic decompression systemaccording to claim 10, wherein the valve-dragging lever can be lifted bythe means of disengagement by 0.2 mm to 0.6 mm.